In general, a storage subsystem is provided with a nonvolatile storage media that can be accessed randomly. Nonvolatile storage media that can be accessed randomly can be, for example, a magnet disk drive, an optical disk drive and the like. Further, the current mainstream storage subsystem is equipped with multiple hard disk drives (HDDs).
Accompanying the progress of semiconductor technology, nonvolatile semiconductor memories that can be used as the storage media of a storage subsystem have been developed. Such nonvolatile semiconductor memory includes, for example, a flash memory. A flash memory is a semiconductor memory that is nonvolatile like a read only memory (ROM), but enabling write such as a random access memory in addition to read. The storage subsystem having a solid state drive (SSD) with a flash memory as the storage media has superior life, power saving property and access time compared to a storage subsystem having only HDDs.
The storage subsystem has a storage controller for controlling data transfer between the host system connected to the storage subsystem and the storage media within the storage subsystem. The storage controller has a front-end interface connecting the host system, a back-end interface for connecting a large number of drives as storage media, a processor for controlling the storage subsystem, a memory connected to the processor, and so on. Further, a “PCI-Express” (hereinafter also referred to as “PCIe”, both being Registered Trademarks) is known as a standard of communication network for connecting the processor, the front-end interface and the back-end interface.
In a prior art storage subsystem, the back-end interface and the plurality of HDDs are connected for example via Serial Attached SCSI (SAS) protocol. Further, the SSD having an SAS interface is also connected to the backend interface.
Recently, an SSD connecting via PCIe to the storage controller with the aim to enhance the performance of the SSD has been provided. Since the PCIe-SSD having the PCIe interface can perform data transfer without having to perform SAS protocol conversion overhead, so that the increase of speed of data transfer is enabled compared to SAS-SSD.
Further, a form factor capable of making the connectors of the HDD having the SAS interface and the PCIe-SSD common to enabling both types of drives mixed within the storage subsystem and to replace the HDD and the PCIe-SSD within the same slot has been standardized.
In order to remove the HDD from the slot of the drive enclosure, it was necessary to remove the HDD from the slot after stopping the rotation of the disk. Therefore, the drive enclosure has LEDs showing the status of power feed to the HDD corresponding to the respective slots to which HDDs are inserted. The operator of the storage subsystem can remove the HDD from the slot when the LED indicates that power supply has been stopped and the stop of rotation of the drive has been ensured.
On the other hand, async removal is considered in PCIe-SSD. Async removal refers to removing the PCIe-SSD from the slot of the drive enclosure without prior notification to the storage controller. Async removal is also called surprise removal.
Non-patent literature 1 discloses an art related to form factor and surprise removal of PCIe-SSD enabling replacement of the HDD and the PCIe-SSD.
Further, non-patent literatures 2 and 3 disclose an art related to async removal of the PCIe-SSD.